University of Vermont
Department of Plant and Soil Science

Fall News Article

THE AFTER EFFECTS OF DROUGHT

Most parts of Vermont and, in fact, much of the Northeast experienced a
drier than usual summer this year. This affected many perennials,
trees, and shrubs. What can you expect now, and in the coming
year, as a result? What can you do to help these stressed plants?

If you have very dry sites, like sandy soil and medians near pavement, or
new plantings, you already may have lost some plants. There's not much
you can do here except replant and help plants get established in future
years. Using organic mulches is a good way to retain soil moisture for the
future.

Don't be too hasty to replace plants that appear to have dried up.
Plants that appear to be dead may actually have living tissue underneath the
bark, or in the ground. Scratch the bark of trees or shrubs to see if
it is still green underneath. It's best to wait, if you can, until
next spring and see if these plants leaf out. The same applies to woody
plants that are living but may appear to have "dead" branches. Again,
use the fingernail test to see if these still have some life. If so,
wait until spring to prune.

For perennials, prune off obviously dead growth and branches. If the whole
plant appears to be dead, mark it to remember its location, as it may
produce new shoots next spring. Browning on the leaves may not be
aesthetically pleasing, but leave them as they are still helping the plant.
Keep perennials weeded, as weeds rob them of soil moisture.
“Deadhead,” or remove, spent flowers from perennials so the plants will
conserve energy from not forming seeds.

Whether you have a sandy or heavier clay soil, top dressing with compost
will help. Generally, the more compost the better. Organic
matter is key to soil health and helping soils to retain more
moisture. This also will help lawns that may have suffered or died
during a drought.

Speaking of lawns, you may wish to rent an aerator or get some aerator
blades for a mini-tiller to help heavy, baked soils. For weak or
stressed lawns on clay, as well as on lighter sandy soils, you might want to
lightly overseed grasses in early fall prior to topdressing lightly with
compost. If seeding, make sure you can keep lawns watered until the
new seeds germinate and begin to establish. Maybe it’s time to consider
whether some of your lawn can be replaced with easier-to-maintain
groundcovers.

Keep all plants watered as well as possible. This means a good
soaking. Light watering fosters shallow roots, which are quite
susceptible to drought. If you have only a few perennials or shrubs,
watering by hand or a slow trickle from the hose may work. If you
can’t water all your landscape if it has been stressed from drought, focus
on new plantings, and on trees and shrubs. Annuals and perennials are
more easily replaced if they succumb to drought.

For a whole perennial bed, soaker hoses often are the best method of
delivery. These are porous rubber hoses that allow water to soak right
into the root area and not on foliage. These don't foster leaf
diseases, and they don't waste water to evaporation and areas without
plants, as do overhead sprinklers. If using overhead sprinklers, water
early in the day to allow foliage to dry before night.

From late September into October, it is especially important to keep
rhododendrons and other evergreens well- watered. This will help them
get through winter with a minimum browning of leaves. If they’ve been
stressed from too little water during summer, this fall watering is even
more important.

The usual rule-of-thumb for watering is an inch of water per week, if not
from rain then from your efforts. Get a rain gauge if you don’t have
one so you’re not fooled. What may appear to be a rainy period, in
reality may not end up delivering sufficient rain. Keep in mind that
when looking at climate numbers, it is the amount and frequency of rain
during a growing season that is important, not the yearly total (which may
have come in just one or a few events).

Don't fertilize woody plants in early fall as this may promote non-hardy
growth, and in late fall it does little good since plants have gone
dormant. However, many herbaceous perennials will respond to fall
fertilizer (an organic, slow release form works well) by going into the
winter hardier and with more food reserves for the following year.

Just keep in mind, too, that what happens one year with woody plants, such
as this year's drought stress, often shows up the following year or even for
several years after. You may see plants with less vigor, increasing
dieback such as from winter injury, or more susceptibility to diseases and
pests. Deciduous trees (those that lose their leaves over winter) which turn
color in fall, such as maples, may turn color much sooner if drought
stressed. It may take several years of proper care and moisture for plants
to fully recover from a very dry summer.

Many woody and herbaceous perennials that bloom early in the season set
their buds the previous year. These include lilacs, forsythia,
peonies, and many daylilies. Even the later bloomers may have less
growth next year as a result of the stresses this year. So, keep an
eye on these and, if they are not at their best this coming year, don't
despair but have patience!

If, in any given year, your plants don't bloom or perform well, ask yourself
what happened last year. Were there stresses? Or, did the plants
bloom quite well and now are taking a year to recoup? Some fruit trees
do this naturally and regularly, a natural process termed “alternate
bearing.” Understanding what happened the year before will help you
provide proper care--and extra help if needed--for your plants this
year.